There are a number of processes described in the literature and patents for recycling NIMH batteries to recover the valuable nickel values contained in them as nickel metal grid, nickel plated foil, the nickel hydroxide in the cathode with some cobalt hydroxide and the nickel metal powder present in the anode as a nickel metal alloy with rare earth metals. Up to now the recovery processes have focused only on the nickel values which allowed for direct smelting of these batteries in furnaces as part of the feed for making high nickel alloys. The rare earth metals react under these conditions to form the rare earth oxides similar to how they are found in nature and end up in the molten oxide slag which is thrown away. More recently, processes have been described where these batteries are carefully melted and the slag volume and nature are controlled to end up with a richer rare earth slag more suitable for recovering the rare earths from the slag in the same way they are recovered by current production processes from rare ores. Another way that is being developed is the total solution of the isolated NIMH electrode materials to produce solutions of the nickel, cobalt and the rare-earth salt mixtures. These solutions are then processed by normal hydrometallurgical methods to separate the solution components into the nickel hydroxide (or carbonate), cobalt hydroxide (or carbonate) and the rare earth separated into a separate mixed rare earth component for processing on a standard rare earth oxide separation process line associated with rare earth ore processing. The reason for this change in the expansion of these recycle processes to recover the rare earth oxides is that the world supply of these oxides is 95% controlled by China and the use for rare earth compounds continues to expand. This has caused supply of rare earth to become tight and probably to remain so with the associated increase in the value of these materials.
The rare earths material are found in the NIMH battery in the unique hydrogen absorbing AB5 metal alloy anode (about 32% are earth metals primarily lanthanum-25%) powder which is the key anode material found in most NIMH batteries. There is a significant amount of energy and loss material in separating then converting a rare-earth ore to the purified rare earth compound mix (25% lanthanum). The correct rare earth oxide mix is converted to the highly reactive rare earth metal mixture (Misch metal) under vacuum and very high temperatures (>1400° C.) under vacuum. This Misch metal then must be mixed with the correct amount of nickel metal and re-melted in a vacuum induction furnace and then cooled rapidly and then ground to a −325 mesh powder under inert atmosphere due to its reactivity. The very hard alloy is difficult to grind. This is a very energy intensive and costly process.
The invention is more preferably used in a cell containing a negative electrode having hydrogen storage alloy materials of the so-called AB5-type, a common example of which is described in the basic formula MsNiAlxMn4Co3 and MsNi5(AlxMn4Co3)x wherein Ms represents a lanthanum-rich misch metal (REM), which includes various rare earth metals and wherein 2.5<r<5.0, 0<s<2.5, 0<t<0.5, and 0<u<0.5. Hydrogen absorbing alloys of this class (i.e., AB5) are disclosed, for instance, in U.S. Pat. Nos. 4,216,274 (Bruning et al) and 4,375,257 (Bruning, et al).
The typical AB2-type materials, as currently envisioned, are based on TiNi2 and typically have the basic atomic structure Ni—Ti—V—Cr—Zr—X—Y wherein X and Y can be other elements of various selection. The invention is more preferably used in a cell containing a negative electrode having hydrogen storage intermetallic alloy materials of the so-called AB5-type, a common example of which are described in the basic formula MmNirCosMntAlu, wherein Mm represents a lanthanum-rich misch metal, which includes various rare earth metals, and wherein 2.5<r<5.0, 0<s<2.5, 0<t<0.5, and 0<u<0.5 and MsNiAlxMn4CO3.
Negative electrode alloys used in NiMH batteries typically comprise La, Pr and Nd as rare earth elements and Zn, Mg and Ni. Cobalt, manganese and aluminum are common additives.
The components of the NIMH battery include nickel metal grid, Ni(OH)2, nickel coated iron, potassium hydroxide electrolyte, and most importantly a nickel metal alloy powder of up to 25-30% by weight. This alloy powder has been developed to absorb considerable hydrogen and is the source of the descriptor “nickel metal hydride” battery. Under charging conditions this nickel alloy absorbs significant amounts of hydrogen as the metal hydride is formed electrochemically. Under battery discharge conditions this absorbed hydrogen reacts electrochemically back to hydroxide and water providing the electrical current of the battery. The currently most well known nickel alloy used is termed AB5 which is an alloy consisting of one part misch metal (mostly lanthanum or REM) to five parts nickel on a mole basis—theoretically 32.1% (REM) on a weight basis. Therefore the naturally occurring rare earth oxide mixture is used to form the misch metal which avoids the expense of separating the rare earth oxides into the individual elements before reducing them to the mixed metal and not to the pure metal such as pure lanthanum metal. This metal mixture is used which is called misch metal. Therefore the AB5 alloy is an alloy of a mixture of lanthanum group metals and nickel with some cobalt and other metals added in small amounts for optimized hydrogen formation and storage. This AB5 component is the most expensive raw material cost for this battery.